Fe₃O₄ NPs modulates the nitrogen metabolism of anammox at low temperature: EPS role and microbial metabolism

Low temperature stress is a main technical bottleneck in anammox process. Supply of Fe₃O₄ NPs is an important strategy in regulating the synthesis of iron-binding protein and nitrogen metabolism of anammox consortia. However, whether Fe₃O₄ NPs can mediate the metabolic mechanisms of anammox at low temperature to enhance nitrogen removal remain unknown. In this work, the role of Fe₃O₄ NPs in coping with low temperature-disturbed anammox was comprehensively explored. Fe₃O₄ NPs directionally enriched Candidatus Kuenenia, which was probably associated with that extracellular polymeric substance (EPS) configuration coping with temperature stress changed from polysaccharide (1021 cm⁻¹) to protein (1637 cm⁻¹). Also, it modulates the unmatched gene activity between hdh and hzs gene, increased nitrogen removal efficiency by 26.32 %. Metagenomics analysis provided the biology evidence that Fe₃O₄ NPs might enter cells by an energy-saving diffusion mechanism. This work would shed the light on the Fe₃O₄ NPs transport and strategy development in low temperature-disturbed anammox.